Bring arducopter higher than tallest structure in the world

I have a goal to fly the arducopter higher than the current tallest structure 829.8 metres and record the flight. I intend on doing this on a calm day but expect winds at high alt. I do not know what speed to expect. Has anyone brought you copter to a high alt of this value and any learnings i can take?

Not sure if you are descending straight down? You might want to avoid direct down descend, this way you avoid prop wash. Try and fly down zig zag flight path down. This way your descend can be extremely fast. Just make sure you never stop the motors from spinning! If the motors stop and start to spin backwards you will not be able to start them again.

I launched mt 3D Robotics Hexa-C copter last week up in the mountains of Virginia and conducted a high speed vertical run for what appeared to be 15-20 seconds in Stablized mode. I was able to see it the entire time and hadn't considered just how high I went until I started my decent. It took a considerable amount of time to bring it down due to not wanting it to flip on descent. I worked my throttle back from roughtly 45% to a minium of about 10% to keep the props turning and still maintaining stability. At one point the copter began to wobble and I had to ramp up RPMs to bring it back to level while descending. I strong discourage anyone not willing to accept risks of flipping and crashing your UAV by maintaining a mimium RPM on your UAV.

My Hexa was equipped with Telemetry, a 5000 maH Lipo, and Gimbal Stablized Hero 2 camera which recorded the entire run. At present due to weight increase to my factory setup, my Lipo on normal flight runs for 8-9 minutes. I did run into a issue with my Quanum Battery Telemetry monitor, I lost signal with the copter's battery somewhere at 150 meters as the copter ran up to 650 meters AGL vertical assent so I am unable to assess how many milli-ampre it took to get to that altitude. I was able to successfully bring it back down and land it, but I forgot to reconnect the battery telemetry to see how much was consumed.

Hope this helps. I have telemetry logs,KMZ file, and video I plan to share later when I get back home from work. Will post for those who are interested.